The present invention relates to a charge-coupled device (CCD), and more particularly, to a CCD image device for enhancing a charge transfer efficiency by minimizing the potential variation of a charge transfer region, which is generated by a channel stop layer (CST) layer.
In general, a CCD is composed of a plurality of photoelectric converting regions for converting the image of light into an electrical signal, a plurality of vertical charge-coupled device (VCCD) region for transferring the image charge generated from the photoelectric converting region in a vertical direction, a horizontal charge-coupled device (HCCD) region for transferring the image charge transferred vertically through the VCCD region in a horizontal direction, and a sensing amp for sensing the image charge transferred horizontally through the HCCD region and transferring the sensed image charge to an external peripheral circuit.
Between each photoelectric converting region and each charge transferring region, in order to prevent the image charge from overflowing into the neighboring pixel and channel, a channel stop layer (CST layer) is formed by ion-implanting a high concentration impurity of a conductivity type opposite to that of a substrate.
Hereinafter, a conventional CCD image device will be described with reference to the attached drawings.
FIG. 1 is a layout diagram of the conventional CCD image device. FIGS. 2a and 2b show vertical potential profiles of the CCD image device of FIG. 1. FIG. 3 show a horizontal potential profile of the CCD image device of FIG. 1.
As shown in FIG.1, the conventional CCD image device comprises a plurality of photodiode regions 1 arranged with a matrix type and converting the image signal of light into an electrical signal, a plurality of vertical charge-coupled device (VCCD) regions 2 formed vertically between the photodiode regions 1 and transferring the image charge generated from photodiode regions 1 in a vertical direction, and a channel stop layer 3 formed between each photodiode region 1 and each VCCD region 2 and preventing the generated signal charge from overflowing into the neighboring pixel.
Photodiode region 1 arranged regularly as described above generate the signal charge according to the wavelength and intensity of the received light.
The signal charge is transferred to VCCD region 2 and transferred vertically in one direction (y-direction of FIG. 1).
The potential profile of the conventional CCD image device will be described below.
Channel stop layer 3 is formed so as to surround photodiode region 1 at a regular interval of "a". This is because the variation and influence of the potential profile by channel stop layer 3 is minimized so that the charge transferring is attained smoothly.
Considering the characteristics of the device, it is possible to form channel stop layer 3 by voluntarily changing the width thereof. Undoubtedly, the width should be the same on the whole.
However, comparing FIG. 2A and FIG. 2b, channel stop layer 3 is formed with a T-shape in the ".alpha." part on the layout, so that it is formed by a space larger than "a " in a horizontal direction. Accordingly, the ion implantation concentration is higher than that of channel stop layer 3 excluding the ".alpha." part".
That is, even if the space of channel stop layer 3 is formed uniformly, the potential profile becomes different in the intersection part of channel stop layer 3 (d1&gt;d2).
That is, in the .alpha." part, there occurs an effect that the ion implantation concentration is increased. Accordingly, the "n" region of photodiode region 1 and the "n" region of VCCD region 2 become narrower in effect.
The horizontal potential profile of the CCD image device of FIG. 1 is shown in FIG. 3.
The difference of the potential caused due to the channel stop layer is little worth consideration in a general camera system.
However, in a system such as a HDTV noticed as the next generation television form, a charge-coupled device more than 200 myriad pixel is necessary, and the charge transfer efficiency attended thereby is required.
Accordingly, the conventional CCD image device having the aforementioned structure requires the improvement of the structure thereof by the following problems.
Referring to FIG. 3, due to the influence of the channel stop layer, the potential distribution of the VCCD narrows in the ".alpha." part and widen in the part excluding the ".alpha." part.
Accordingly, first, since the potential distribution of the VCCD is not uniform, the charge transfer efficiency becomes lower when transferring the signal charge.
Secondly, the "p" region of the channel stop layer encroaches on the "n" region of the photodiode region and the "n" region of the VCCD region, thereby reducing the area of the entire light-receiving region and the transfer channel region. Accordingly, it is much disadvantageous to the miniature and high integration of a chip. This is because, as the size of the device becomes smaller and the integrating thereof becomes higher, the ununiformness of the potential distribution in the transfer channel is a main factor of deteriorating the device characteristics.